I took the index of your words, transformed the quantity to binary, included a few zeros, calculated the sha256 digest, took the first part of the hexadecimal to transform it to binary, added three zeros on the eight digits from the binary and bought 00000010011 which interprets to 19 in https://livebackpage.com/story4214359/bip39-seed-phrase-mnemonics-generator-an-overview